[Old Tele man]

...where's the shark teeth? She's gotta have those Flying Tiger "Shark Teeth" so she can scare the wind aside to let her "...slide thru the air..." with the greatest of ease!

...my wife has an '04 Vibe 1.8L (1ZZ-FE) with the 4-speed automatic, so I've been reading this WHOLE saga with interest. BTW, my car is an '09 Vibe 1.8L (2ZR-FE) also with the 4-speed overdrive automatic...although both are 1.8L engines, they're totally different with different bore & stroke and different fuel delivery systems.

...way back in 1981, I cut lexan covers for our '81 Ford Escort for aerodynamic reasons, but wasn't really able to quantify and measure differences in mpg...looked cool though.

...back in the 1950's the "moon" hub caps (full disc) were the rage for any car attempting Bonneville time trials, for exactly the same reason today's "pizza" platters are popular (after eating the pizza of course)...aerodynamics!

...have you thought about an adjustable grill (louver) opening? With maybe a hand rotary crank (or push-pull) actuation? During COLD weather you close it up (like truckers do with their snapable radiatior blankets), then open it up during HOT weather just enough to maintain acceptable coolant temperature?